The present invention relates to releasable anchors for semi-submersible vessels for offshore drilling and in particular to the disengagement of the tethers which fasten tension leg platforms to the sea bed.
A tension leg platform is a semi-submersible vessel which is anchored by means of a number of tethers tensioned against the natural buoyance of the vessel. Each tether comprises a hollow drill string with an anchor connector at its lower end for locking into a template fastened to the sea bed. It is necessary for the anchor connector to be releasable from the template, and for this to be controlled from the vessel, so that the lower connector may be serviced or the vessel moved to a new location.
The anchor connector is generally released by disengaging the mechanical locking mechanism using hydraulic pressure transmitted down the bore of the tether. However, it has been found that in some instances, for example when the connector has been in the locked position for some years the pressure necessary to unlock the locking mechanism is so great that it causes permanent damage to the joint between the tether and the anchor connectot. This is clearly undesirable.